Observation and Analysis of the Ground Water in Nijima Island

Homma, M.; Ogihara, Kunihiro; Shindo, Shizuo

doi:10.2208/jscej1969.1974.222_79

Cited by 2 publications

(8 citation statements)

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“…Holocene pyroclastic surge deposits form a single-layered unconfined aquifer in the study area. The measured hydraulic conductivity (K) of the aquifer was reported to be between 1 × 10 −6 and 6 × 10 −3 m/s (Construction Section of Niijima Village, 2001;Honma et al, 1974;Shindo, 1980). Aichi et al (2011) estimated K to be 3.0 × 10 −4 to 3.4 × 10 −2 m/s based on the water level fluctuation of wells by tidal signals.…”

Section: Hydrogeological Settingsmentioning

confidence: 99%

“…Previous studies (Aichi et al, 2011;Honma et al, 1974) indicated that water table elevations ranged from about 0.5 m a.m.s.l. near the coast to 1.3 m a.m.s.l.…”

Section: Hydrogeological Settingsmentioning

confidence: 99%

“…The groundwater system is recharged by direct infiltration of rainfall. The recharge of the aquifer was estimated to be around 30% to 50% of the annual rainfalls (Honma et al, 1974). Groundwater is abstracted from public wells in the central plain of the island, supplying about 3.7 × 10 5 m 3 of freshwater annually for nearly 3,000 residents that mainly dwell in Honson Village (Figure 1c) (Oshima Subprefecture of Tokyo, 2014).…”

Section: Hydrogeological Settingsmentioning

confidence: 99%

“…Porosity of 0.34 was obtained from Shindo (1980). According to Honma et al (1974), the recharge rate of the groundwater system of Niijima Island was equivalent to 30% to 50% of the annual rainfall amount. Therefore, a constant recharge rate R(t) = 883 mm/year was adopted in the baseline case, which was derived from 40% of the average annual rainfall amount of 2,207 mm/year (Japan Meteorological Agency, 2017).…”

Section: Parameterization and Settings For Variable Scenariosmentioning

confidence: 99%

“…To study how the length of ST‐3 would affect the simulation results, Cases 11 and 12 with the period of ST‐3 of 1 and 30 days, respectively, were simulated. According to Honma et al (), the main aquifer of Niijima Island received freshwater recharge of 30% to 50% of the annual rainfall. Therefore, keeping the R / K ratio constant, besides the baseline case, which set R ( t ) to be 40% of the annual rainfall, two additional cases with R ( t ) of 30% and 50% of the annual rainfall were designed, namely, R ( t ) = 662 mm/year with K = 8.1 × 10 ‐4 m/s for Case 13 and R ( t ) = 1,104 mm/year with K = 1.3 × 10 ‐3 m/s for Case 14.…”

Section: Numerical Modelsmentioning

confidence: 99%

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Future Risks of Tsunami‐Induced Seawater Intrusion Into Unconfined Coastal Aquifers: Insights From Numerical Simulations at Niijima Island, Japan

Liu

Tokunaga

2019

Water Resources Research

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Tsunami-induced seawater inundation causes vertical seawater infiltration into coastal aquifers and induces unexpected salinization of fresh groundwater resources. Assessing future risks of seawater intrusion in tsunami-prone areas can provide essential information supporting disaster preparedness. In this study, we investigated seawater intrusion and aquifer recovery processes under the future Nankai earthquake and tsunami scenarios at Niijima Island, Japan. A groundwater model with a 2-D vertical cross section was developed to solve variable-density flow and salt transport in unsaturatedsaturated media using the numerical code, FEFLOW. Our simulation results indicate that the unsaturated zone behaves as an initial storage of the infiltrated seawater and controls the maximum amount of seawater infiltration during the anticipated tsunami inundation. The bedrock structures affect the direction of seawater movement in the saturated zone and the flushing time of the polluted aquifer. Our analysis suggests that the tsunami inundation height, the rainfall recharge rate, and hydraulic conductivity are the primary sources of uncertainties in the simulation results. These findings have implications for other tsunami-prone zones with respect to the understanding of the relevant physical processes and model uncertainties. Key Points: • Unsaturated zone initially stores infiltrated seawater during tsunami inundation and constrains the mass of infiltrated salt to subsurface • Bedrock structures affect the directions of seawater migration after tsunami inundation because of the contribution of density-driven flow • Tsunami inundation height, rainfall recharge rate, and hydraulic conductivity are the primary sources of model uncertainties Correspondence to:

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Section: Hydrogeological Settingsmentioning

confidence: 99%

“…Previous studies (Aichi et al, 2011;Honma et al, 1974) indicated that water table elevations ranged from about 0.5 m a.m.s.l. near the coast to 1.3 m a.m.s.l.…”

Section: Hydrogeological Settingsmentioning

confidence: 99%

Section: Hydrogeological Settingsmentioning

confidence: 99%

Section: Parameterization and Settings For Variable Scenariosmentioning

confidence: 99%

Section: Numerical Modelsmentioning

confidence: 99%

See 3 more Smart Citations

Future Risks of Tsunami‐Induced Seawater Intrusion Into Unconfined Coastal Aquifers: Insights From Numerical Simulations at Niijima Island, Japan

Liu

Tokunaga

2019

Water Resources Research

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3D modeling of tsunami-induced seawater intrusion and aquifer recovery in Niijima Island, Japan, under the future tsunami scenario

Liu

Tokunaga

2020

Journal of Groundwater Hydrology

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A 3D numerical model was developed to simulate seawater intrusion and aquifer recovery in Niijima Island under the future Nankai earthquake and tsunami scenario. The FEFLOW code was used to solve density-dependent groundwater flow and mass transport in unsaturated-saturated porous media. The simulations indicated that the maximum amount of seawater intrusion during the tsunami was controlled by the total unsaturated void space of the soil beneath the inundation area. After the tsunami, directions of seawater movement and flushing time depended on the pre-tsunami groundwater flow conditions and bedrock structures. Some groundwater was found to be survived from salinization, and showed the potential to provide water supply in an equivalent amount of the pre-tsunami level without worsening the recover y process. The simulated attempt to remove the intruded seawater from a polluted well could accelerate aquifer recovery but might not be practical due to the cost of maintaining intensive pumping over years.

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Observation and Analysis of the Ground Water in Nijima Island

Cited by 2 publications

References 0 publications

Future Risks of Tsunami‐Induced Seawater Intrusion Into Unconfined Coastal Aquifers: Insights From Numerical Simulations at Niijima Island, Japan

Future Risks of Tsunami‐Induced Seawater Intrusion Into Unconfined Coastal Aquifers: Insights From Numerical Simulations at Niijima Island, Japan

3D modeling of tsunami-induced seawater intrusion and aquifer recovery in Niijima Island, Japan, under the future tsunami scenario

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